Recently, with the development of electronic and micro-electronic technologies, colors play a more and more important role in data storage and display, and the adjustment and control of colors are one of the major features of modern display technology. Colors of many living beings in nature, such as colors of beetles' elytra and butterflies' wings, are derived from their microstructures. Research suggests that the microstructure of beetles' elytra is similar to that of cholesteric liquid crystal. The unique helical structure of cholesteric liquid crystal determines its special optical properties, such as selective reflection, circular dichroism and the like. When the wavelength (λo) of an incident light is matched with the pitch (p) of a cholesteric liquid crystal, that is, λo=n×p, (n is the average reflectivity of the cholesteric liquid crystal), the light is reflected and the reflected light is a circularly polarized light, the rotation direction of which is in conformity with the helical structure of the cholesteric liquid crystal. Therefore, the wavelength of the reflected light can be adjusted by changing the reflectivity and pitch of the liquid crystal. Cholesteric liquid crystal has a responsive behavior to external stimulus, and because of this behavior, cholesteric liquid crystal is widely used in the fields of filter, information storage, display and the like.
Cholesteric liquid crystal is generally formulated from a nematic liquid crystal and a chiral additive, because chiral additive can induce the transformation of nematic liquid crystal to cholesteric liquid crystal. Therefore, chiral additive plays an important role in nematic liquid crystal. With respect to a chiral additive, helical twisting power constant (HTP) is a key parameter to evaluate its twisting capacity, and is defined as:p=1/(HTP×Xc)wherein, p is the pitch of a cholesteric liquid crystal, and Xc is the concentration by mass of a chiral additive in the host liquid crystal material. The HTP value depends on the nature of the chiral additive itself. When p is constant, the greater the HTP value of the chiral additive, the less the amount of the chiral additive in the host liquid crystal material is, which is beneficial for improving the properties of the cholesteric liquid crystal.